/*
cdecoder.c - c source to a base64 decoding algorithm implementation

This is part of the libb64 project, and has been placed in the public domain.
For details, see http://sourceforge.net/projects/libb64
*/

#include "libb64/cdecode.h"

int base64_decode_value(int value_in) {
	static const int decoding[] = { 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1,
		                            -1, -1, 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10, 11, 12, 13, 14, 15, 16, 17,
		                            18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31,
		                            32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51 };
	static const int decoding_size = sizeof(decoding) / sizeof(decoding[0]);
	value_in -= 43;
	if (value_in < 0 || value_in >= decoding_size)
		return -1;
	return decoding[value_in];
}

void base64_init_decodestate(base64_decodestate* state_in) {
	state_in->step = step_a;
	state_in->plainchar = 0;
}

int base64_decode_block(const char* code_in, const int length_in, char* plaintext_out, base64_decodestate* state_in) {
	const char* codechar = code_in;
	char* plainchar = plaintext_out;
	int fragment = 0;

	*plainchar = state_in->plainchar;

	switch (state_in->step) {
		while (1) {
		case step_a:
			do {
				if (codechar == code_in + length_in) {
					state_in->step = step_a;
					state_in->plainchar = *plainchar;
					return plainchar - plaintext_out;
				}
				fragment = base64_decode_value(*codechar++);
			} while (fragment < 0);
			*plainchar = (char)((fragment & 0x03f) << 2);
		case step_b:
			do {
				if (codechar == code_in + length_in) {
					state_in->step = step_b;
					state_in->plainchar = *plainchar;
					return plainchar - plaintext_out;
				}
				fragment = base64_decode_value(*codechar++);
			} while (fragment < 0);
			*plainchar++ |= (char)((fragment & 0x030) >> 4);
			*plainchar = (char)((fragment & 0x00f) << 4);
		case step_c:
			do {
				if (codechar == code_in + length_in) {
					state_in->step = step_c;
					state_in->plainchar = *plainchar;
					return plainchar - plaintext_out;
				}
				fragment = base64_decode_value(*codechar++);
			} while (fragment < 0);
			*plainchar++ |= (char)((fragment & 0x03c) >> 2);
			*plainchar = (char)((fragment & 0x003) << 6);
		case step_d:
			do {
				if (codechar == code_in + length_in) {
					state_in->step = step_d;
					state_in->plainchar = *plainchar;
					return plainchar - plaintext_out;
				}
				fragment = base64_decode_value(*codechar++);
			} while (fragment < 0);
			*plainchar++ |= (char)((fragment & 0x03f));
		}
	}
	/* control should not reach here */
	return plainchar - plaintext_out;
}
